Natural background levels

The presence of radiation in the workplace - which is an inevitable consequence of the radioactivity of uranium - requires that additional safety precautions be taken over and above those observed in other similar workplaces. There are generally three sources from which radiation exposure may occur (i) radiation emitted from uranium ore in-situ and/or during handling (ii) airborne radiation resulting from the decay of radon gas released from the ore and uranium dust and (iii) contamination by ore dust or concentrate. Radiation levels around uranium mining and milling facilities are quite low - for the most part only a few times the natural background levels - and they decrease rapidly as the distance from... 

Exposure Levels in Humans. Although some data on the levels of americium in human tissues exposed to natural background levels (food, water, and air) are available, few measurements have been made on the americium content in human tissues. The principal source of information about occupationally exposed individuals is the U.S. Transuranium and Uranium Registries (USTUR) Tissue Program and database, established to document levels and distribution of uranium and transuranium isotopes in human tissues for occupationally exposed workers (USTUR 1999). Several major database files are available. 

When a sample of the same Kevlar-29 fabric was identically treated in l 02-atmosphere except in the absence of photolysis (in the dark) for 24 hours, the results of C02 evolved at 25° and 196°C from the GC-analysis were the same as the samples under photolysis (e.g., Table I). However, the gross difference was in the analyses of the GC-mass spectroscopic data, where no oxygen-18-labelled C02 isotopes evolved (i.e., there was no C02 or 48co2 above the natural background levels). ... 

On the other hand, the estimated risk for occupants of residential structures cleaned up to the EPA guideline values was about a factor of 3 higher than for residents exposed to natural background levels. 

Anthropogenic use of mercury should be curtailed, because the difference between tolerable natural background levels of mercury and harmful effects in the environment is exceptionally small... 

KEYWORDS stream sediment, natural background levels, chemical fluxes, phase analysis, historical mine waste... 

The country-wide dataset of stream sediment analyses in Austria consists of 36,136 samples analyzed for 34 chemical elements (Fig. 1), (Thalmann et al. 1989). Complemented by local surveys of hydrochemistry, whole rock geochemistry, soil chemistry and mineralogical phase analyses, these data are used to derive natural background levels of different rock units, investigate chemical fluxes between soil, rock and groundwater, and evaluate the emission risks of historical mine waste. 

While the first method gives a quick visual overview of ranges, the second, more sophisticated method leads to a more detailed correlation. In both cases, the correspondence between stream sediment and whole rock geochemistry is not perfect since sediments represent only the weathered product of rocks (Pfleiderer et al. 2008). Lithologically homogeneous areas away from mining sites or mineralization are used to derive natural background levels. 

Fig. 2. Derivation of natural background levels by (a) superimposing sample points on geological units (left) and by (b) relating sample points to catchment areas (right).

The long-term uses of lead explain why this element should be so widely dispersed in the environment. In this regards one should answer the question as to what is the natural background level of lead. At present this is a question of controversy. Lead... 

A distinction sometimes needs to be made between the natural background level of a substance, which arises purely as a result of natural processes, and the ambient background level, which is the concentration measurable in the environment at a pristine site (see Section 5.10). In practice, a pristine site is often considered to be one that does not receive any direct inputs from local sources, although it needs to be accepted that for many substances there may be an appreciable input from diffuse atmospheric sources. 

Radiation other tlian radon Estimated 360 cancers per year. Mostly from building materials. Medical exposure and natural background levels not included. 

The NCRP recommends an annual effective dose for continuous members of the public in some circumstances of 1 mSV (100 mrem). This value is in addition to natural background level of irradiation approximately twice that (2mSv 200 mrem). In this context, the NIRL was taken to be 1/100 of this level, or 0.01 mSv/year (1 mrem/year). This level of exposure was low enough to have a risk of <1 cancer/1,000,000 and the risk for lung cancer <1/10,000,000. The notation is negligible individual dose (NID) (Harley 2001, 2008). 

EPA 1985j). Groundwater from an aquifer adjacent to a uranium mill tailings pile in Falls City, Texas, was also found to have concentrations of uranium above natural background levels (DOE 1994). 

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